The invention relates to a transparent electrode, for example a panel for a liquid crystal or touch-sensitive or other visual display. In general, a liquid crystal display will comprise two such panels with a liquid crystal therebetween. The function of the panels is to apply an electric field across the liquid crystal, thereby causing a change in its reflectivity or other optical properties. One such panel will need to be transparent in order that the change in, for example, reflectivity be viewed and it is with such a panel that the invention is concerned. The other panel may also be transparent.
The panel must be able to be connected (which includes capacitive connection) to a voltage source and may have elements of a shape corresponding to the information that is to be displayed. In general the elements will comprise a plurality of cells, generally substantially rectangular for example square, that can be powered in a variety of combinations to produce the outline of letters and numbers etc. Another type of display acts as a shutter, allowing information behind it to be selectively viewed. The elements may comprise a conductive transparent material, such as indium-tin oxide (represented as ITO, but generally having the composition In.sub.2 O.sub.3 plus SnO.sub.2) that are connectable to the voltage source via a conductive metal bus. Such bussing is generally necessary due to the difficulty of making a transparent material of sufficiently high electrical conductivity to avoid undesirable voltage drop along the leads that supply the elements with power.
The standard prior art method of making such a structure is to apply a silver loaded ink to a panel using a silk-screening process, after which the ink is cured by heating. The conductive silver is thus applied in the pattern desired in the finished product. There are, however, several disadvantages inherent in this method. Firstly, the heat curing step is inconvenient and limits the choice of backing to which the ITO is applied to materials that can withstand high temperatures. Secondly, silver inks applied by this method adhere poorly to ITO. a third disadvantage is that the size of the conductive interconnections is limited using the silk-screening technique. A fourth disadvantage is that conductive silver inks do not have high conductivity unless they are thick. Also, chemical stability of such silver plus organic binder paints may be insufficient.
We have discovered that the disadvantages of the prior art can be overcome using a simple etching process. Whilst etching is known in general in the context of liquid crystal displays, see for example U.S. Pat. No. 4,523,811 to Ota, a satisfactory two step deposition followed by an etching process has not been disclosed for the production of bussed transparent conductive elements. U.S. Pat. No. 4,523,811 is concerned with the production of non-linear, metal-insulator-metal, structures that are located at and used to control individual display elements based on glass substrates, the intention being to increase the display capacity of the liquid crystal device by means of active multiplexing. The pixels, or elements, are thus very small. Various selective etching techniques are disclosed to produce the non-linear metal-insulator-metal structures.